Metal Matrix Composites (MMC) are a class of materials wherein a reinforcing filler is interdispersed with a metal phase. See Rohatgi, Defense Science Journal, Vol. 43, No. 4, October 1993, pp 323-349. In the preparation of one type of MMC material, particulate ceramic reinforcing filler is mixed with a molten metal and then the mixture is cooled to form an MMC article. In the preparation of another type of MMC material, a porous ceramic preform comprising a ceramic reinforcing filler is infiltrated with a molten metal and then the metal-filled preform is cooled to form the MMC article. MMC's tend to be stiffer and stronger than metals but more ductile than ceramics.
In general, in order to achieve high performance in an MMC made by mixing a ceramic reinforcing filler with a molten metal and then cooling the mixture to form the MMC article, there should be: (a) good wetability of the ceramic reinforcing filler by the molten metal; (b) good chemical stability of the ceramic reinforcing filler in the molten metal; (c) good dispersion of the ceramic reinforcing filler in the molten metal; and (d) good adhesion between the ceramic reinforcing filler and the metal after the MMC is formed.
In general, in order to achieve high performance in an MMC made by wetting a preform with a molten metal and then cooling the metal-filled preform to form an MMC article, there should be: (a) good wetability of the ceramic reinforcing filler of the preform by the molten metal; and (b) good adhesion between the ceramic reinforcing filler and the metal after MMC is formed.
Ceramic reinforcing fillers that perform well in MMC's (for example, titanium diboride or titanium carbide mixed with molten aluminum or porous boron carbide preforms infiltrated with molten aluminum) are relatively expensive resulting in significantly increased cost of an MMC article. Ceramic reinforcing fillers that are relatively low in cost tend to perform poorly in MMC's. For example, alumina (Al2O3) and silica (SiO2) are relatively low cost reinforcing filler materials but neither silica nor alumina are wetted by molten aluminum. Alumina reinforcing filler particles tend to agglomerate in molten aluminum instead of being well dispersed while silica reacts in molten aluminum to form Si rich Al and Al2O3. It would be a substantial advance in the MMC art if the relatively low cost ceramic reinforcing fillers of the type that are not wetted by molten aluminum could be used to produce lower cost, high performance MMC's